The present invention relates generally to the conversion of the photonic energy of light into mechanical work in the form of dynamic motion of a mechanical structure. More particularly, this invention pertains to an apparatus and methods for generating rectilinear, curvilinear, or rotational movement of a mechanical structure by controlling the illumination of a light directed upon a new type of photosensitive body having photomechanical characteristics. Even more particularly, this invention pertains to a bimorphic polymeric photomechanical apparatus and method for converting light into movement.
Progress in the development of optic fiber technology and compact laser light sources has brought to life a great variety of optical sensors for almost every trade. Fiber optic based sensors have been incorporated into “smart” materials and structures, such as “smart skins”, etc. Polymeric “smart skin” materials provide the useful structural properties characteristic of polymers while permitting exploitation of the electronic and photonic properties of miniaturized optical sensor systems. However, these systems lack simple and compact actuators that can be driven by the same low power light radiation used to operate the optical sensor systems. Current solutions employ electrically-driven actuators, which require voltage and current to be delivered by wires from an electric power source. The optical signal still must be converted into an electric current that can control the electrically-driven actuator. The fast growing industry of optical switching also experiences a similar problem. Currently available optical switches typically employ either electrically-driven piezoelectric actuator elements requiring external high voltage for actuation or converse piezoelectric driven actuator elements requiring a high power density light to cause actuation. These optical switches need either a relatively high power light source or external high voltage source to be applied to a switch.
The prior art is illustrated in the photo-driven actuator previously described by Uchino in “Recent topics of ceramic actuators. How to develop new ceramic devices”, Ferroelectrics, Vol. 91,281–292 (1989). This prior art actuator is based on the photostrictive effect exhibited by piezoelectric lead lanthanum zirconate titanate (PLZT) ceramics in the presence of ultraviolet light. Shining ultraviolet light on a single PLZT body will not make the material move greatly. Instead, a complex arrangement of paired wafers is needed to magnify the displacement. Two very thin layers of PLZT are bonded together with opposing polarization directions and conducting material connecting the edges. Light shone on one wafer creates expansion and an electric field that goes through the conducting material and is applied on the second layer. The voltage triggers the piezoelectric effect in the second layer, which contracts, bending the entire double wafer. Unfortunately, when the illumination is shut off, it can take several minutes for the material to return to its original shape, so, in order to have any kind of quick response system, the second wafer must be illuminated to cause the shape change in the other direction.
The disadvantages of this and the other prior art are significant when designing a useful, low power photo-driven actuator or photo-driven fast acting switch. The body of the photosensitive material is made of solid piezoelectric PLZT ceramics and is hard to shape and mold. The PLZT actuator must be driven only by UV radiation, such as 380 nm and shorter wavelength, produced by high power high pressure arc lamps or UV lasers. UV radiation has significant attenuation losses when delivered through conventional optic fibers. The response of the PLZT actuator is very slow (several seconds). The maximum mechanical displacement generated by PLZT ceramics in response to illumination by light is short since the ceramic is hard, brittle, and has low strain before it fractures. As a result of these factors, PLZT ceramics' conversion efficiency of light energy into mechanical work is low.
Thus, there is a great need for a simple, efficient, and compact actuator, which can be driven by low power light radiation in the visible or mid-infrared range delivered through conventional optic fibers. The actuator should be suitable for integration with optical sensors and optical actuators of the same or different type. What is needed, then, is a photomechanical actuator as described herein.